Thermal switch and the like



Oct. 31, 1939. J. SCHMIDINGER THERMAL SWITCH AND THE LIKE Filed April 50, 1957 3 Sheets-Sheet l R a m Wm N 0 N mm m T m; w 5 H w 5 7 0 Jwfi Oct. 31, 1939. J sc mm 2,177,671

THERMAL SWITCH AND THE LIKE Filed April 30, 1937 3 Sheets-Sheet 2 IN VEN TOR.

Oct. 31, 1939. J. SCHMIDINGER THERMAL SWITCH AND THE LIKE a Shets-Sheet 3 Filed April 30, 1937 MEI/097W Mug? A TTORNEYS.

Patented Oct. 31, 1939 UNITED STATES PATENT OFFICE THERMAL swrrqn AND THE LIKE Joseph Schmidingcr, New Yon-h, N. Y. Application April 30, 1937, Serial No. 139,932.

\ 9 Claims.

This invention relates to thermally operated switches, relays and the like.

One object of the invention is a novel switch or relay of the above indicated character embody- 5 ing a multiple turn resistance wire or coil, the, expansion and contraction of which are utilized 15 a very slight expansion or contraction of a thermo-responsive element is amplified to a large switch movement and particularly such a structure which is characterized by its simplicity of construction and minimum parts.

20 A further object of the invention is a novelthermal switch whose operation isnot disturbed by external shocks or vibrations.

I A further object is a switch of this character which may be operated with extremely small cur- I 25 rents.

A further object of the invention is a switch of the .above indicated character having snap action and a long life.

A further object of the invention is a novel thermal switch of the above,indicated character having a delayed hot wire action.

A further object of the invention is a thermal switch of the above indicated character which is characterized by its small and compact size, its 35 simplicity in construction, and the ease and economy with which it may be manufactured.

Further objects of the invention will hereinafter appear.

For a better understanding of ,the invention, 0 reference may be had to the accompanying drawings forming a part of this application wherein: Fig. 1 is a side view of one embodiment of the thermal switch of this invention;

Fig. 2 is a plan view thereof; 5 Fig. ,3 is a circuit diagram illustrating a use of the switch shown in Figs. 1 and 2;

Figs. 4, 5 and6 are diagrammatic views showing modifications of the invention;

Fig, '7 is a diagrammatic view indicating rough- 50 ly the operation of the strip in these modifications; 1

Fig. 8 is a view of a modified form of strip; and Figs. 9, 10 and 11 show modified structures. Referring to the drawings, the invention is 55 illustrated as embodied in a thermal switch which is mounted upon a supporting frame or base i which may be either of insulating material or metallic. The switch or relay comprises a U shaped member 2 having legs 3 and 4 and this ,U-shaped member is made of a strong resilient 5 metal, as, for example, of spring steel wire. Each of the legs 3 and 4 is provided with an insulating sleeve 5 of glass, ceramic or any other suitable insulating materialhaving suflicient strength for the purpose. 'A cdil of very fine resistance wire 10 6 is wound around and bound about the sleeves 5, one end 1 of the wire being fastened and electrically ,connected with a terminal 8, and the other end 9 of the coil being electrically connected at H) with the leg 4 of the U. The wire 5 coil 6 of fine resistance wire is wound under tension around the legs 3 and 4 of the U- member, while the legs 3 and 4 are sprung toward each other against'the inherent spring tension therein, so that when the resistance 'wire coil 6 is heated and caused thereby to expand, the legs 3 and 4 are permitted to spring outwardly from each other to the extent permitted by the expanding coil. The resistance wire of the coil 6 may be of any of the conventional types found on the market and the number of turns depends upon the voltage applied, the size of the wire, etc. and'this particular embodiment of coil .is adaptable to be connected across a 110 volt circuit. The dotted position shown in Fig. 1 indicates the resiliency of the spring legs 3 and 4, namely, the relative positions the legs 3 and 4 would assume if entirely free from the resistance wire coil 6. v

A metallic strip i 2 is welded or otherwise securely fastened at its ends to the legs 3 and 4 at points between the wire coil 6 and the base plate I. In the particular embodiment shown in Fig. 1 this strip i2 is of uniform width and strength throughout and is welded or fastened to the legs 3 and 4 in a manner to cause it to assume the bowed position indicated in Fig. 2 and corresponding to the room temperature of the coil 6. The strip l2 carries a contact I! which co-operates with another contact member I3. The latter is mounted in an insulating sleeve [4 of glass or other suitable insulatin'g material, and this sleeve or insulating support I4 is carried by an angle piece l5 which is firmly secured at one end. to'the sleeve and on its other end to the leg 4 of the U-member, the angle support l5 being conveniently disposed just above the baseboard I. The contact i3 is electrically connected through the resistance IS with a terminal II.

The U-member 2 is mounted upon and supported by the base or frame at a single p .int of support and in the particular embodimentshown in Figs. 1 and 2 this single point 01' support is the lower end of the leg I. The whole thermal mechanism, including the U- member 2, the strip I2, contact l3 and the resistance coil 6 is thereby rendered immune in its operation to strains, distortion and warping of the frame or support I. It is also less likely to be disturbed by external shocks and vibrations. The end of the leg 4 is electrically connected with a third terminal l8.

In Fig. 3 is illustrated diagrammatically one of the many uses to which the thermal switch of Figs. 1 and 2 may be adapted. Here it is used as a delayed hot wire relay switch for protecting an incandescent filament lamp 22 against excessive voltages and currents. This incandescent lamp is indicated as connected in circuit with devices 2|, which upon the initial closure of the switch 22 permit an excessive voltage to be applied to and excessive current to flow through the filament incandescent lamp 20. These devices 2| may represent radio tubes, for example. The thermal switch functions to cut out a protective resistance l6 which is connected in shunt to the incandescent lamp 22 at the initial closing of the switch 22. Thus, with the resistance coil 6 connected across the circuit as indicated and with the control switch 22 open, the bowed strip 2 connects in circuit the shunt resistance |6..

Upon the'closure, however, of the switch 22, the resistance coil 6 heats up and is caused to expand which permits the resilient spring legs 2 and l.

of the U-member to straighten out the strip |2 sufilciently to break the shunt resistance circuit.

Before this interruption takes place, the devices 2| reach the operating condition wherein only the normal voltage and currents are supplied to the incandescent lamp 2!. A resistance 22 isshown connected in series with the devices 2| and the lamp Ill. The resistance coil 6 may remain in the circuit as long as the devices 2| are to the resistance 22 and other elements of the circuit connected across the line I! in order to prevent excessive current passing through the incandescent lamp 22.

In Figs. 4 to 6 I have illustrated the device of my invention adapted to give a definite and strong snap action. The strip 22 here corresponds to the strip i2 of Figs. 1 to 3 and like strip I2 is firmly fastened or welded at its ends to the legs 2 and l of the U in a manner to cause the strip to be bowed and buckled as shown. The strip 20 is observed to have a reverse curvature, comprising the two concave parts 22 looking upwardly at the drawing and the central convex part 2|. The central part 2| carries a contact l2 which in one position engages the stop or contact 22 and in another position engages the contact or stop 22. In the cold position the contact 22 engages the contact or stop 22 and in the hot position the contact 22 engages the stationary contact or stop 24.

Fig. 7 shows diagrammatically approximate positions assumed by the strip 22 in the normal operation. The full line position indicates the strip 22 in the positionwherethe contact 22 engages the stationary contact or stop 22 which corresponds tothe room temperature position of the switch. The dotted line posit on indicates roughly the position of the strip 20 with the contact 22 in engagement with the stationary contact or stop 24, which corresponds to the heated position of the switch and the maximum permitted separation of the ends of the legs 2 and 4. The parts 22 of the strip 20, during the heating of the coil ,6 and the springing apart of the legs 2 and I, are gradually flattened out with increasing radii of their curvatures to permit the snapping of the intermediate part of the strip past the dead center from the contact or stop 22 to the contact or stop 24. The dot and dash position indicates an intermediate position assumed by the parts 22 oi the strip 20 when the resistance coil 6 is being cooled and the legs 2 and 2 are being drawn towards each other by the contracting coil. Here it is observed that the parts 22 of the strip are first caused to be bowed upwardly with curvatures having decreased radii, and this upward bowing oi the parts 22 ultimately causes the reverse curved part 2| to snap downwardly against the contact or stop 22.

Figs. 4 to 'I show, as indicated above, one way of bowing and constraining the strip 20 toobtain the snap action. This may be effected by upsetting the intermediate portion 2| of the strip 22 from the full bowed and constrained position position indicated in dotted lines, but a contact or stop 22 is positioned below the dotted line position to arrest the strip before the reverse curvature 2| is eliminated. With .the intermediate part 2|, therefor, of the strip resting against the contact or stop 22 which corresponds to the heated condition of the switch, the intermediate part 2| may be caused to snap back to a position in engagement with the contact or stop 22 by interrupting the circuit through the coil 2 and cooling the same. During the cooling operation the ends of the strip 20 are brought closer to each other and the effect of this compression is the tendency of the central portion 2| of the strip to at first bear more tightly against the stop or contact 22. As the cooling and contracting progress, however, with the stop or contact 22 preventing further upward movement of the central portion 2|, the additional compression results in the buckling of the end portions of the strip as shown in Fig. 7 which finally causes the intermediate portion 2| to break down by a snap action and assume a position against the lower stop or contact 22. It is ob served that the first movement of the bowed parts 22 of the strip 22 is in one ""direction (downwardly) when the coil 2 is being heated and in the opposite direction (upwardly) when coil 6 is being cooled. In the'modifications Figs. 4 to 7 the strip 22 may be either of the uniform dimensions and strength as shownin Figs. 1 and 2, or it may have its intermediate portions weakened as shown in Fig. 8, but the construction in Fig. 8 is preferred where the snap action is desired. As shown in Fig. 8, the strip 22 may be of uniform thickness throughout and the intermediate portions weakened by progressivelymarrowing the strip 22 from the ends towards center where air-1,071 i in the particular embodiment shown the contact I! is mounted. The weakening of the intermediate portions of the strip 33, as'indicated, fa-

cilitates the snapping function, namely, the ability of the strip 30 to snap from one equitened and constrained at both ends, it may be positioned at any other convenient position of the strip 30 which moves through an amplitude suflicient to control contacts. It, is also understood that while the preferred construction is that shown in Fig. 8, the weakest portion of the strip may be at some other position than that at the middle point and the weakening may take any other form than that illustrated.

In Fig. '1 the relative positions of the legs a and '4 of the U-member are illustrated at the three diiferent operating conditions and this is correct whether the U-member 2 is mounted and supported at a single point by fastening the end of one of the legs to the base I, or whether it is mounted by fastening the same to the base i from any other single point,. as for example by mountingit at a point on the cross member bridging legs 3 and 4.

In the circuit of Fig. 4 the thermal switch functions as a relay, with the, resistance coil 6 and terminals 40 and 4| connected across any suitable supply circuit together with any control switch for cutting in and out the coil. Whenthe coil is out of circuit the controlled circuit is completed through 42 and 43, and when the coil Kiss in circuit to heat the coil 6 the circuit controlled ls'from 42 to 44.

-In the circuit of Fig. 6 the strip 33 and the controlling contact 34 are connected in shunt with the coil 6 and, accordingly, when the circuit is completed through contacts 45 and .46 the resistance coil 6 is in circuit but is automatically shunted when it heats up and causes the strip 30 to snap over into engagement with the contact 34.

33 but upon heating up, due to the passage of. current through the coil 3, the strip 30 is caused to snap over into engagement with the stop 34 to interrupt the circuit; but as soon as the room temperature is approached or reached, the circuit is again completed withthe snap action at the contact 33. r

While I have shown the coil6 as being directly heated by the passage of electricity therethrough, it is understood that this coil 6 or its-equivalent may be externally heated, as for example by the association therewith of a separate ,heating element, as shown in Fig. 10. Here a flexible wire .40 is welded. or otherwise readily fastened at 4L to the legs 3 and 4 of the U,.these legs being held in the full line position by the wire against the naturaltendency of the legs to spring relatively'to each other, the coilthaving terminals accuracyat all times.

3', as illustrated, for externally heating the wire 43 to cause the expansion of. the same. If desired, a sleeve of insulated material 42 maybe disposed between the coil 6 and the expansible wire 4|. It is understood that the heating coil 3 is suitably connected in circuit to effect eitherthe slow acting switch of Figs. 1 to 3 or to effect the snap action switch of Figs. 4 to 7, or any other circuit may be utilized for causing the control strip I! to control the contacts or circuit desired. In this modification the U instead of being mounted at the single point on the end of the leg 4 is mounted upon the base or frame support at 45 being a point intermediate the cross piece bridging the legs 3 and 4. Here, as in Figs. 1 and 2, the whole unit is carried at a single point whereby the unit is rendered immune to external disturbing forces and effects.

Fig. 9 shows the mounting of a thermal switch, such as shown in Fig. 2, at a single point 45 intermediate the legs 3 and 4 as shown in Fig. 10.

In Fig. 11 the U comprising the legs 3 and 4 is also mounted at a single point intermediate the legs 3 and 4 as indicated in Figs. 9 and 10. In-

stead of the heating resistance coils 8 bound 25 around the legs ,3, and 4 of the U a single expansible tension wire 50 is fastened at either end to the legs 3 and 4 to hold them in a position tobow or buckle the strip l2. The wire 50 is electrically and mechanically fastened at one end to the leg 4 as indicated at 5|. It is electrically insulated from the leg 3 but mechanically fastened thereto by means of a glass head 52 fused about thewire and disposed in an eyelet 53 conveniently formed'in the leg 3 oi theU. The wire 50 upon expansion by connecting the same in circuit and heating the same permitsthe legs, 3 and 4 to-spring apart under their resiliency and upon cooling to control the contact strip IL. The

.strip l2of Figs. 9, 10 and 11 is indicated 01' uni-- form strength throughout, but it may be of the character shown in Fig. 8. The device of Fig. 11 maybe utilized to control any circuit, as for example any of the above circuits shownin Figs. 3 to 6.

Figs. 1 and 2 indicate the compactness of the whole device by comparison of the size of the terminals with the thermal mechanism itself. The single point of mounting of the mechanism on a frame or support renders, as described above,-the whole mechanism substantially free of externaldisturbance and, accordingly, when the mechanism is once adjusted it operates indefinitely with It may be economically manufactured on a quantity production basis and its simplicity in mechanism,-parts and operation is obvious. The leg 4 in the modification shown being fixed, the only moving parts of the mechanism are the leg 3 and the strip I 2 which simplifies the construction and operation 4 of the switch. The strip or vane i2 is in continuous restraint and is rigidly fastened at both ends to the supporting leg 4 and the relatively moving leg 3 and-this construction-also assists in rendering the mechanism less subject to outside shocks and influence. In the preferred embodiment the contact l3 and its support I! are carried by the U member, but it may in certain cases be mounted directly upon the base I. In Fig. 7 the relative movements of the mem bers 3 and 4' is exaggerated for convenience in illustration. In actual practice the relative movement of these leg members 3 and 4 is exmediate part of the strip 30. For example, I have been able to obtain an amplification of from 1 to to 1 to 25, the possible amplification being greater with the strip constrained as in Figs. 4 to 6 to assume the reverse curvatures at the different points of the length thereof. As an indication of the sensitiveness of the mechanism I have been able to produce automatic snap switch action of the strip 30 with a heating current as low as 2 milliamperes.

I claim:

1. A thermal switch of the character set forth comprising a frame support, a U-resiiient spring member, a multiple turn resistance coil bound about the legs of said U-mer'nber 'and causing the same to assume positions against the inherent resiliency thereof, a control strip rigidly fixed to the legs of the U, and a contact mounted upon said U-member and cooperating with said strip, said U-member being mounted upon and fastened at a single fixed point to said frame.

2. In a thermal switch of the character set forth a frame support, a U-resilient spring member, an electrically heated expansible wire fastened to the legs of the U-member and holding the same against their springing outwardly under their inherent resiliency, a controlled strip rigidly fixed at its ends to the legs of the U and flexed so as to assume a curved form and a contact mounted upon said U-member and cooperating with said strip, said U-member being mounted upon ,and fastened at a single fixed point of support to said frame.

3. In a device of the character set forth, a main support and a thermal electric switch control mechanism mounted thereon, said mechanism comprising a frame support member, and a thermal responsive device and a pair of switch contacts controlled thereby, said contacts and said device being mounteddirectly upon said frame support member, and said mechanism including the frame support member being fastened to and mounted upon said main support at a single point of support. I

4. A thermal control switch of the character set forth comprising a U-resilient spring member, an electrically heated expansible wire fastened to the legs of said U-member and restraining the outward movement of the legs against the natural resiliency thereof, and a circuit control strip bridging and rigidly fastened to the legs of the U, said strip being constrained to assume a curved form with the portions adjacent the ends thereof bowed transversely of the legs in one direction and the middle portion thereof bowed in the opposite direction, and stops disposed on the opposite sides of the middle portion of the strip to limit the movement thereof.

5. A thermal switch of the character set forth comprising a U-resilient spring member, an electrically heated expansible wire fastened to the legs of said U-member and restraining the outward movement thereof against the natural inherent resiliency and a controlled strip bridging and rigidly fastened to the legs of the U, said strip being constrained to assume a curved form with a portion thereof bowed in one direction laterally of the legs and another portion thereof bowed in the opposite direction laterally of the legs, and stops disposed in the path of one of said how portions of the strip to limit the movement thereof.

6. In a thermal switch of the character set forth in claim 1 wherein the U-member is mounted and supported upon the supporting frame by means of one of the legs.

7. In a thermal switch of the character set forth in claim 1 wherein the contact is carried by one of the legs of the U. 8. In a thermal switch of the character set forth, a frame support, a U shaped resilient spring member, an electrically heated expar'isible wire fastened to the legs of the U member and holding the same against their springing outwardly relatively to each other under' their inherent resiliency, a controlled strip. rigidly fastened at'its ends to the legs of the U and flexed so as to assume a curved form, said U member being mounted upon and fastened at a single fixed point of support to said frame and a contact cooperating with said strip.

9. In a thermal switch of the character set forth, a support having at least one resilient spring member, an electrically heated expansible wire rigidly fastened at both ends to said support,

' one end of the resilient member and holding the same against its springing outwardly relatively to the other part of the support, a controlled strip also rigidly fastened at both ends to the support, one end being fastened to the resilient .member and the strip being flexed so as to assume a curved form and a contact co-operating with said strip for controlling an electrical circuit.

' JOSEPH SCHMIDINGER.-

CERTIFICATE OF CORRECTI'ON.-

Patent 'No. 2,177, 67

October 1959 JOSEPH SCHMIDINGER. I It is hereby certified thaderror appears in the printed specification of the above numbered patent requiring correction'as follows: Page 11,, sec- 0nd column, line l claim 9, for'the word "of" read -.to and that the ea id Letters Patent should be read with this'correction therein that the same may conform to the "record of the case in the Patent Office.

Signed and sealed this 1mm day of May, a. p. 191,0.

(Seal) Henry Van Arsdal e, Acting Commissioner of Patents. 

